Glucocorticoid receptors in intact cells can be inactivated to a state that does not bind steroid and then rapidly reactivated to a steroid binding state. The process of inactivation appears to involve a dephosphorylation and reactivation a phosphorylation of either the receptor protein itself or an associated binding factor. Activation in cytosol preparations is stimulated by a heat stable factor that also stabilizes the unbound receptor to inactivation by incubation at 25 degrees. In the proposed work we will focus on the purification and characterization of the heat stable factor. A second focus is to demonstrate transfer of radiolabeled phosphate from ATP to a steroid-binding moiety.